Patent GB-666070-A (GB)
Title: Search signal apparatus for determining the listening habits of wave signal receiver users
IPC: H04H1/00
Filed: 1948-10-25
Abstract: 666,070. Radio receiving apparatus. NIELSEN CO., A. C. Oct. 25, 1948 [Oct. 24, 1947; Oct. 24, 1947; Oct. 24, 1947], Nos. 27737/48, 27738/48, and 27739/48. Class 40 (v). In a device for determining the listening habits of radio receiver users, a central station is located in a position remote from the receiver and comprises a generator which cyclically generates a search signal varying in frequency throughout the search cycle which produces a response at the receiver, the instant of occurrence of the response during the search cycle being indicative of the particular transmitter to which the receiver is tuned, and a filter and amplifier attachment at the receiver transmits the response to the central station for automatically recording the information on a moving element. The receiver 10, Fig. 2a, is provided with an attachment 13, operation of the switch 22 of the receiver supply unit also energizing a relay 111 to switch on the supply unit 110 for the attachment. This energizes a 9 kc. oscillator 121 whose output is connected to the house wiring circuit 14 and by this means a signal is conveyed to a circuit 144, 145, tuned to 9 kc. at the central station 15, Fig. 2c, to cause a gas discharge tube 138 to strike and energize the relay 137 to switch on the supply unit 120. The unit 120 includes a rectifier 150 for high-tension supply and a rectifier 164 for providing biasing potential. The search signal generator 35, Fig. 2b, includes a crystalcontrolled oscillator 35a whose frequency is variable in steps corresponding to the frequencies of the transmitters likely to be received, by crystals 43a ... 43f connected to the rotary switch 45, the output of the oscillator being connected to an aerial 16 and controlled by a rotary switch 56 whose movable arm is connected to the H.T. supply, the switches 45 and 56 being mechanically coupled to a switch 64, which selects a stylus 67a ... 67i appropriate to the transmitter being received, and driven at one r.p.m. by a synchronous motor 61. To provide information relating to frequency modulated stations a unit 35b comprises three V.H.F. oscillators 70 having their outputs connected to an aerial 82 and controlled by the switch 56. The output from a 5 kc. oscillator 89 is applied to the grid of a valve 84 in the cathode circuit of the oscillator valve 70 so that the output of the V.H.F. oscillators is pulsed at a frequency of 5 kc., the output of the oscillator 89 also being applied to the oscillator 35a to provide a modulated output. At the receiver a connection is made from the volume control 32 to the input of an amplifier 175, having filter circuits sharply tuned to 5 kc., in the receiver attachment 13, the output of the amplifier being connected to the mains 14 so that the response produced in the receiver when the search signal generator is at the frequency of the station being received is transmitted to the central station 15. Alternatively a microphone positioned near the loudspeaker 12 may provide the input to the amplifier 175. The central station is provided with a 5 kc. filter 184, Fig. 2c, connected to the mains through the contacts of relay 137, whose output is applied to an amplifier 189a, rectifier 190a, and D.C. amplifier 191a, to energize the stylus control relay 193, closing of contacts 193a supplying potential to the switch 64 to cause the appropriate stylus 67a ... 67i to mark a continuously moving sheet of electrolytic paper 215 driven by a motor 217, a stylus 67j marking the tape all the time to give an indication of stations other than those provided for in the search signal generator. In the " continuous scanning " position of the manual switch 208, as shown, the motor 61 is energized all the time, but in the alternative dotted line position the signal generator is prevented from operating once a station has been tuned in by the receiver, the contacts 193b and 193c of the relay 193 deenergizing the motor 61, the "all other stations " stylus 67j, and the signal generator 35, and the contacts 193a applying a positive potential to the anode of the valve 190a to maintain the relay 193 energized. To start the signal generator recycling when the receiver 10 is tuned to another station, in the receiver attachment 13 an integrating circuit 230 is connected to the volume control 32 to provide a voltage equivalent to the change in automatic gain control, which is applied to an L.F. amplifier 234, whose output is connected to a polarized relay 238 normally biased to the intermediate position. If the A.G.C. voltage changes, one of the contacts 238a or 238b is made and the output from an 8 kc. oscillator 240 is applied to the mains 14. At the central station 15 an 8 kc. filter 245 connected to the mains through the contacts of relay 137 applies the signal via an amplifier 189b, rectifier 190b, and D.C. amplifier 191b, to operate a relay 202 which de-energizes the relay 193, and brings into operation the search signal generator. In order that operation of the A.G.C. by a strong search tone due to reception of a distant station will not operate the re-cycling device, the anode of valve 191a is connected through a condenser 260 to a resistor 261 in the grid circuit of valve 189b, so that at the instant of operation of the relay 193 the re-cycling amplifier is prevented from operating the relay 202, contacts 202b discharging the condenser 260 when re-cycling commences. As an alternative to using the A.G.C., the tuning control or push-buttons may be provided with a permanent magnet associated with a coil, movement of the tuning control, inducing a current for initiating the re-cycling of the signal generator. In an alternative arrangement, Figs. 4a and 4b (not shown), the search signal generator is cyclically varied as before by motor-driven switches by the stylus control is driven by another synchronized motor which is stopped when the 5 kc. signal is received at the central station, the channel of the signal generator coinciding with the frequency to which the receiver is tuned then being earthed, and the search signal continuing to be produced on all other channels. Specification 541,079 is referred to.